Cigarette filter

ABSTRACT

A cigarette filter means is constructed to provide a pair of elongated, high surface area, cavities defined on opposite sides of a relatively thin wall formed of filtering material. Preferably, only the ends of the filter means contact an overwrapped outer tube which provides maximum available surface area to provide a filter element with a relatively high filtration efficiency and satisfying ordinary commercial standards regarding &#39;&#39;&#39;&#39;taste,&#39;&#39;&#39;&#39; pressure drop and manufacturing cost. The filter comprises an outer elongated member in which an inner crimped filter is disposed. The latter has major portions of the outer surface spaced from the inner surface of the outer member to define cavity means therebetween into which the smoke is compelled to pass.

United States Patent Inventors Richard M. Berger Richmond; Elwin W.Brooks, Mechanicsville, both of, Va. Appl. No. 820,355 Filed Apr. 30,1969 Patented Aug. 17, 1971 Assignee American Filtrona CorporationRichmond, Va.

Continuation-impart of application Ser. No. 727,477, May 8, 1968, nowPatent No. 3,533,416, dated Oct. 13, 1970.

6/1963 Davidson 131/10x 10/19 67 L1oyd... 131/10.7x

Primary Examiner- Melvin D. Rein Attorneys-Holman & Stern and Samuel L.Davidson ABSTRACT: A cigarette filter means is constructed to provide apair of elongated, high surface area, cavities defined on opposite sidesof a relatively thin wall formed of filtering material. Preferably, onlythe ends of the filter means contact an overwrapped outer tube whichprovides maximum available surface area to provide a filter element witha relatively high filtration efficiency and satisfying ordinarycommercial standards regarding taste," pressure drop and manufacturingcost. The filter comprises an outer elongated member in which an innercrimped filter is disposed. The latter has major portions ofthe outersurfacespaced from the inner surface of the outer member to definecavity means therebetween into which the smoke is compelled to pass.

PATENTED mm 1 Ian 31; 599 '54s SHEET 1 [IF 3 INVENTORS RICHARD M. BERGERELWIN W. BROOKS BY Jm Ma i M ATTORNEYS SHEET 30F 3 PATENTEU mm 1 anINVENTORS RICHARD M. BERGER ELWIN W. BROOKS Y MZZM /M ATTORNEYSCIGARETTE FILTER Thisapplication is a continuation-in-part of copendingapplication Ser. No.'727,477, filed May 8, I968, for Tobacco SmokeFilter, now US. Pat. No. 3,533,416 granted on Oct. 13,1970.

This invention relates to filters, particularly filters for tobaccosmoke. Known filters differ in their resistance to air flow throughthem. This resistance is usually expressed as the pressure drop in cm.water gauge when air at a flow rate of 17.5 cc./se c. is passed throughthe filter. The retention of tobacco smoke solids is expressed as thepercentage of such materials retained by the filter when the smoke ofone cigarette is drawn through it. Filters at present in commercialproduction comprise packed rods of bonded filaments or fibers, gatheredpaperwebs or bonded particulate adsorbents. The pressure drop andretention of such filters is approximately proportional to their length.Such filters cannot provide a retention of greater than 55 percentwithout an excessive pressure drop. Filters comprising a laminar memberenclosed within a tube and having diaphragms, baffles or other barriersto direct the smoke from one face to the other of the laminar member,are

known. Such filters may have a higher retention and lower pressure dropthan the current commercial filters. However the assembly of the partsof such a filter is difficult and this, it is believed, is the reasonwhy such filters have not been produced commercially. It is an object ofthis invention to provide a filter comprising a laminar filtering memberwhich may havea high retention and a low pressure drop and which will beeconomical to manufacture and to provide a method and apparatus formanufacturing the same. This invention provides a tobacco smoke filterelement comprising an axially extending tubular outer member, withinsaid member an axially extending hollow inner member comprising anaxially extending air permeable wall, the arrangement being such thatsmoke passing in an axial direction must travel through said wall ofsaid inner member and be filtered thereby characterized in that theoutersurface of the wall of the inner member is in engagement with theinnersurface of the outer member at a first axial position so assubstantially to preclude axial passage of smoke between the members,and at a second axial position the inner surfaces of the wall of theinner member are in engagement so as substantially to preclude axialpassage of the smoke between them at the said second position.

The tubular outer member is formed of a material to provide sufficientrigidity for handling in conventional filter cigarette machines. It maybe of plastic, paper, cardboard or bonded fibers. The wall of the innerhollow member is formed of air permeable materials, for example, filterpaper or bonded fibers such as crimped cellulose acetate fibers, porousplastic, plastic foam, blends of paper fibers with thermoplastic fibersespecially secondary cellulose acetate fibers. Enclosedby or retainedwithin the material of the inner member, adsorbent materials for theremoval of vapor phase constituents of tobacco smoke, for example activecarbon, or-materials for flavoringthe smoke, may be provided. Thus it ispossible to produce-a filter with high retention for both vapor phaseconstituents and tobacco smoke solids.

In the drawings FIG. Ishows a typical'filter with a portion of a tobaccorod attached.

FIG. 2, shows an apparatus for formingthe filter of the invention.

FIG. 3 shows a strip offilter material during conversion into an innerhollow member.

FIG. 4.shows a stage in.the production of a pair of filter cigarettes;

FIGS. 5, 6, 7 and 8 are perspective-views of three different I forms ofthe innerfiltering member.

FIG. 9 shows an apparatus for forming a filter from cellulose acetatefilaments.

FIG. 10 is an enlarged view of part of the apparatus of FIG. 9.

The invention will now be described in an embodiment. In FIG. 1 aportion of a filter cigarette 20 comprises a paper wrapped tobacco rod22 and a filter 30 secured to each other by a tipping overwrap 32. Thefilter 30 includes a tubular outer member 34 and a hollow inner member36. Member 34 comprises a cylinder of stiff paper of the type usedin themanufacture of cigarette mouthpieces. The member 36 comprises an airpermeable tube, the wall of which is of bonded cellulose acetate fibers,or of one of the other filtering materials described herein. One endportion 38 is cylindrical and is in engagement around the whole of itsperiphery with the inner surface of outer member 34 therebysubstantially preventing passage of smoke at this point between members34 and 36. An adhesive may be used to secure end portion 38 as well asto seal it more effectively to member 34. Integral portions 42 of innermember 36 are crimped as described hereinafter so that the innersurfaces thereof are in engagement. Thus the inner member'36 divides anupstream cavity 40 from a downstream cavity 48. Tobacco smoke comingfrom tobacco rod 22 passes into cavity 40 through the perme able wall ofinner member 36 into cavity 48. The position of filter 30 may bereversed so that cavity 48 faces the tobacco rod 22. The edges 44 of thecrimped portion 42contact the inner surface of outer member 34 andassist in positioning the inner member 36 within the outer member 34 andensuring that the permeable wall of the inner member 36 between portions38 and 42 is available for smoke filtration. Alternative forms ofcrimping are shown in FIGS. 5, 6, 7 and 8. The inner surfaces of thewalls of member 36 are engaged at 42 so as substantially to precludepassage of smoke between them. They may, when the material of the wallsis at least partly thermoplastic, be fused to each other and the part 42made impervious by coalescence. However, for the purposes of thisinvention, the surfaces are sufficiently engaged if the smoke isdirected substantially to pass through the portion 46 of wall of member36 lying between the parts 38 and 42. Likewisethe parts 38 aresufficiently engaged with the inner surface of member 34 if there is nosignificant bypass of smoke between them, though complete sealing isclearly desirable.

In FIGS. 5 and 6 alternative forms of crimp in the inner member 36 areshown. The support given to the outer member 34 by the Y-shaped orcruciform ribs is better than that given by the simpler S or Z crimpshown in FIG. 1.

In FIG. 7 a further alternative form of inner member 36 is shown. Inthis the walls of member 36 are crimped so as to leave ribs which arearranged helically around the longitudinal axis of the member 36. Bythis means good support is given to the outer member 34 and the crosssection of the latter may, when it is made of thin materials, be keptsubstantially circular.

In FIG. 8 an embodiment is shown of the inner member 36 having a flaredportion 38 and a closed end 42 formed by twisting.

In a further embodiment the inner member 36 of FIGS. 1 5, 6, 7 and 8-maybe made in a double form shown for example by the dotted lines with thecrimped portion 42 lying midway between the ends of the filter. Thisembodiment providesa circular end, which facilitates attachment to acigarette and a circular recessed end next to the mouth, which ispreferred by many smokers. This form facilitates the incorporation ofgranules of adsorbent or other material. These may be placed in thespace around the crimped portion 42 of the inner member 36, and retainedin place by outer member34 and the two circular ends 38.- The materialcontributes to the radial rigidity of the filter rod at this part of itslength.-

The outer member 34 may, if desired, be dispensed with and its functionperformed by the use of a stiff tipping overwrap 32; The use of thisembodiment is dependent upon the provision ofa cigarette filter machineable satisfactorily to handle the crimped inner member 36.

By lengthening the filter, the area of-the permeable wall of the innermember 36 may be increased and the pressure drop reduced thereby.Additional filtering materials 52in granular form may be located withinthe cavity 48 and retained therein by a permeable disc 50, therebyproviding a three element filter comprising the inner member 36, thematerial in the cavity 48 and the disc 50. Such granular materials mayinclude activated carbon, silica gel or other adsorbents. Alternativelythe cavity 48 may be closed by a plug 51, shown by the dotted lines.

In the embodiment of FIGS. 2 and 3, a method and means for formingfilter elements, of the type shown in FIG. 1, from a stripof web ofmaterial is shown. A web of filtering material such as paper or like airpermeable material comes from roll 62, passes to a tubular gamiture 64wherein it is brought into cylindrical form by an endless belt 66 so asto form a tube 68. The edges 70 of the web are joined by overlapping orbutting as shown at 72 and may be adhered and sealed to each other by amolten plastic material coming from a nozzle 74. Stripes 76 of anadhesivematerial such as a molten plastic may be applied at spacedlocations on one side of the web by a reciprocating intermittentlyacting dispenser 78. The stripes 76 may be axially spaced a distanceequal to the length of a single filter or twice this length. The tube 68thus has the stripes on its inner surface. A crimper 80 hasreciprocating shaped jaws within it, which crimp the tube 68 into a formsuch as is shown in FIGS. 1, 5, and 6, and seal the molten plastic so asto form a continuous rod 86 of the crimped inner element comprisingalternating crimped and hollow portions. Other adhesives such as heatseal or liquid adhesives may be used'in place of the molten plastic, inwhich case heated jaws in the crimper'80 are employed to bring the innersurfaces o the tube 68 into engagement.

The crimped element 86 is then overwrapped with a strip of heat sealpaper coming from reel 88 by means of a further garniture 90. This hasthe conventional drive belt 92 and heater 96-for forming a longitudinallapped and stuck seam to secure the strip around the inner element 86. Acut off 100 divides the combined inner and outer elements 98 intomultiple length filter rods I02. These may include four filter elementswhich may be subdivided into the double unit 94 in FIG. 4 which is shownattached to tobacco rods 108, by a tipping overwrap 110. A cut at line112 severs the double unit with the tobacco rods 108 into two filtercigarettes.

Other'tec'hniques for forming the inner element from a web or strip,include helical winding. In this process, which is commonly used for themanufacture of cardboard tubes, oneor more strips are helically woundand adhered at overlapping portions to each other around a mandrel. Morethan one layer of material may beused, thus'it is possible to producethe inner hollow member with inner and outer layers of differentmaterial. For example, the inner layer may comprise athermoplasticmaterial for facilitating thesealing of the crimped portions 42 by theapplication of heat. Heat may additionally be used to bond thethermoplastic layer to the adjacent layer. Other materials may beincorporated in one or more of the layers, to provide specificfiltering, chemical or flavoring effects.

The hollow inner element may also be formed by a laminate. This is aconvenient way of incorporating a thermoplastic inner layer by themethod of FIG. 2. The sealing of the-longitudinal margins 70 of thestrip of filtering material and of the crimped portions 42 of the innerelement are, in this case, effected solely by the application of heat.The filtering material of the inner member may comprise thermoplasticand a nonthermoplastic fiber in admixture, for example, a sheet ofporous paper formed of pulp fibers and secondary cellulose acetate.

In the embodiment of the invention shown in FIGS. 9 and 10, a known towpreparation device indicated by block diagram 130, supplies opened,crimped, continuousfilamentary cellulose acetate two 132, having about 9percent triacetin in fine droplets distributed upon its surface, to anair nozzle 134. This is generally as shown in British Pat. No. 933,227and comprises two frustoconical tubes, fixed one inside the other,having a supply of compressed air applied to connection 136 to pass inthe space between the frusta and escape from the end 138, thus drawingthe tow 132 with it. A mandrel, not shown, passesthrough nozzle 134 intojet 140. The latter is generally as shown in British Pat. l\ lo. 970,817and is provided with a supply of. steam to connection 142. The steampasses into the bore of the nozzle through radial orifices and serves tobond the filaments of cellulose acetate to each other as they passthrough the annulus between the mandrel and the bore. Thus a tube 156 ofbonded cellulose acetate filaments is formed. This passes into a crimper144 which'comprises a heated enclosure 146 within which is a chain 148carrying crimping devices 150 shown in FIG. 10. Each of the devicescomprises a block 152 having a slot 154 for receiving the tube 156coming from jet 140. Four sliding spring loaded dies 158 having endsdirected towards the rod 156, are shaped to cooperate to produce thedesired form of crimp in the tube, for example, that shown in FIG. 6.The cellulose acetate flows under heat to adhere the filaments to eachother and form and retain thedesired shape. The crimped tube 160 comingfrom the crimper 144 then enters the garniture 162 which is.of knownform and includes an endless belt 164 driven by a' drum 166. A paperstrip 174 envelops the crimped tube 160, which now forms the hollowinner member, to form the outer member as described in the embodiment ofFIG. 2. A cutoff 168 divides the rod 170 into plugs 172 of any desiredmultiplicity of filter units. To incorporate granular material, thepaper strip 174 is formed into a trough around the member 160 as shownby the-dotted line, and granules are dropped from a hopper 176 so thatthey flow around the member 160 and fill up the space between it and thepaper strip 174. The latter is then folded around the member 160andsealed with a lapped and stuck seam by heater 178 to form a compositerod. The cutoff 168 is timed to cut only through the uncrimped parts ofthe member 160. i

In acomparative trial, filters of the type shown in FIG. 1 were madefrom commercially available air permeable papers having differentpressure drops. Each filter was 25 mm. long and was attached to atobacco rod 65 mm. long. Table I compares the percentage retention ofthese filters, with filters made according to the prior art processes.Myria is a longitudinally grooved paper filter, Acetate is theconventional filter made of crimped continuous filaments of celluloseacetate. The filter of this invention can be seen to be much moreretentive at a given pressure drop.

In Table II a comparison is made of a filter made in accordance withFIG. 1, having a coating of activated carbon on its inner surface, witha conventional filter plug of the same length of bonded carbon madeaccording to the prior art. Acrolein is chosen as a typical vapor phasecompound, the removal of which from tobacco smoke by the filter,indicates its vapor phase retentivity. This invention in a single filterprovides, at a low pressure drop, a high retention of vapor phaseconstituents with a high retention of tobacco smoke solids.

Filter The area of the filtering material through which smoke is drawnin filters of this invention may be varied. Generally it lies between 3and 16 cm'. The packed filters of the prior art have an area equal tothat of the end of the cigarette, that is about 0.5 cm. In consequenceof the greater area, the filtering material may have a greater packingdensity, that is the ratio of the volume of the solid material in thefiltering material, to the'total volume of the material. The packingdensity may lie between 0.1 and 0.4, preferably about 0.35. A packingdensity of this magnitude has not so far been used for the filtration ofcigarette smoke. The velocity of the smoke stream through the filter atthe normal puffing rate may lie between 2.5'and-5.7 ems/second. Thismuch lower velocity permits filtration to be more effective at any givenpressure drop than with the prior art commercial filters. Particularlygood results are obtained with fibers of a diameter below 25 microns,fibers around 14 microns diameter having proved particularly effectivein making theinnerrnember sufficiently rigid and retentive, while stillretaining an acceptably low pressure drop. that is not greatly in excessof6 cms. water gauge.

The filter and method of its manufacture have. been described above,principally in terms of the preferred materials and apparatus. Howeverit is apparent that simple trial in accordance with the principlesdisclosed in the embodiments will show the suitability of othermaterials. Thus,-for example, other thermoplastic filaments and fibersmay be used instead of cellulose acetate, and paper made from syntheticplastics may replace the paper of the embodiment of FIG. 2'. Likewise inplace of the continuous rod method of FIGS. 2 and 9, a method involvingthe sequence of forminga permeable tube, cutting it into lengths, anddeforming them to bring their inner surfaces into engagement, could beemployed.

We claim:

l. A filter means including a filter element comprising a. an axiallyelongated outer member;

b. an axially elongated inner member disposed withinsaid outer member;

c. said outer member including an inner surface, and an outersurface andhaving spaced end portions;

d. said inner member comprising a filtering material and including aninner surface and an outer surface and having spaced end portions;

e. integral peripheral portions of said outer surface of said innermember being juxtaposed to portions of said inner surface of said outermember to at least substantially preclude axial passage of smoke acrossthe area therebetween;

f. the major portions of said outer surface of said innerv member beingspaced from said inner-surface of said outer member to define firstelongated cavity1meanstherebetween; g. integral first portions of saidinner member defining a first area extending across the interior of saidinner member which offers at least as much resistance to passage of Vsmoke as said filtering material, said first portions being axiallyspaced from said peripheral portions;

h. second portions of said inner member defining a second area extendingacross the interior of said inner member 1 which offers less resistanceto passage of smoke than the area between said peripheral portions ofsaid inner member and said inner surface of said outer member, saidsecond portions being axially spaced fromsaid first portions toward saidperipheral portions; 1 1 I the interior of said inner member betweensaid first and second portions defining second elongated cavity means,whereby smoke passing through said filter element between opposite endsthereof must travel through both said cavity means and through saidfiltering material;

j. the area of the wall of the inner member through which smoke is drawnlying between 3.0 and 16.0 cm.

2. A filter means including a filter element comprising a. an axiallyelongated outer member;

b. an axially elongated inner member disposed within said outer member;1 i

c. said outer member including an inner surface and an outer surface andhaving spaced end portions;

d. said inner member comprising a filtering material and including aninner surface and an outer surface and having spaced end portions;

. integral peripheralportions of said outer surface of said inner memberbeing juxtaposed to portions of said inner surface of said outer memberto at least substantially preclude axial passage of smoke across thearea therebetween;

f. the major portions of said outer surface of said inner member beingspaced from said inner surface of said outer member to define firstelongated cavity means therebetween;

integral first portions of said inner member defining a first areaextending across the interior of said inner member which offers at leastas much resistance to passage of smoke as said filtering material, saidfirst portions being axially spaced from said peripheral portions;

. second portions of said inner member defining a second area extendingacross the interior'of said inner member which offers less resistance topassage of smoke than the area between said peripheral portions of saidinner member and said inner surface of said outer member, said secondportions being axially spaced from said first portions toward saidperipheral portions;

. the interior of said inner member between said first and secondportions defining secondelongated cavity means,

whereby smoke passing through said filter element between opposite endsthereof must travel through both said cavity means and through saidfiltering material;

j. the wall ofthe inner member comprising filtering materi al, thepacking density -of which lies between 0.1 and 0.4

3. A filter means including a filter element comprising:

a. an-axially elongated outer member;

b. anaxially elongated inner member disposed within said outer member;

c. said outer member including an inner surface and an outer surface andhaving spaced end portions;

d.- said inner member comprising a filtering material and including aninner surface and an outer surface-and having spaced end portions; e.integral peripheralportions of said outer surface of said inner memberbeing juxtaposed to portions of said inner surface of said outer memberto at least substantially preclude axial passage of smoke across thearea therebetween;

f. the major portions of said outer surface of said inner member beingspaced from said inner surface of said outer member to define firstelongated cavity means therebetween;

g. integral first portions of said inner member defining a first areaextending across the interior of saidinn'ermember which offers at leastas much resistance to passage of smoke as said filtering material, saidfirst portions being axially spaced from said peripheral portions;

h. second portions of said inner member defining a second area extendingacross the interior of said inner member which offers less resistance topassage of smoke than the .area between said peripheral portions of saidinner member and said inner surface of said outer member, said secondportions being axially spaced from said first portions toward saidperipheral portions;

. the interior of said inner member between said first and secondportions defining second elongated cavity means, whereby smoke passingthrough said filter element between'opposite ends thereof must travelthrough both said cavity means and through said filtering material;

j. the wall of the inner member comprising substantially of fibershaving a diameter of less than microns.

4. A filter means including a filter element comprising a. an axiallyelongated outer member;

b. an axially-elongated inner member disposed within said outer member;

c. said outer member including an inner surface and a outer surface andhaving spaced end portions;

d. said inner member comprising a filtering materialand including aninner surface and an outer surface and having spaced end portions; v e.integral peripheral portions of said outer surface of said inner memberbeing juxtaposed to portions of said inner surface of said outer memberto at least substantially preclude axial passage of smoke across thearea therebetween;

f. the major portions of said outer surface of said inner member beingspaced from said inner surface of said outer member to define firstelongated cavity means therebe'tween;

g. integral first portions of said inner member defining a first areaextending across the interior of said inner member which offers at leastas much resistance to passage of smoke'as said filtering material, saidfirst portions being axially spaced from said peripheral portions;

h. second portions of said inner member defining a second area extendingacross the interior of said inner member which offers less resistance topassage of smokethan the area between said peripheral portions of saidinner member and said inner surface of said outer member, said secondportions being axially spaced from said first portions toward saidperipheral portions;

. the interior of said inner member between said first and secondportions defining secondelongated cavity means, whereby smoke passingthrough said filter element between opposite ends thereof must travelthrough both said cavity means and through said filtering material;

j. the pressure drop being not greater than 6 cm. water gauge.

5. A filter rod comprising a plurality of filter means integrally joinedin end-to-end relationship for subsequent separation, said filter meanscomprising;

a. an axially elongated outer member;

b. an axially elongated inner member disposed within said outer member;

c. said outer member including an inner surface and an .outer surfaceand having spaced end portions;

d. said inner member comprising a filtering material and including aninner surface and an outer surfaceand having spaced end portions;

e. integral peripheral portions of said outer surface of said innermember being juxtaposed to portions of said inner surface of said outermember to at least substantially" preclude axial passage of smoke acrossthe area therebetween;

. the major portions of said outer surface of. said inner member beingspaced from said inner surface'of said outer member to define firstelongated cavity means therebetween;

g. integral first portions of said inner member defining a first areaextending across the interior of said inner member which offers at leastas much resistance to passage of smoke as said filtering material, saidfirst portions being axially spaced from said peripheral portions;

h. second portions of said inner member defining a second area extendingacross the interior of said inner member which offers less resistance topassage of smoke than the area between said peripheral portions of saidinner member and said inner surface of said outer member, said secondportions being axially spaced from said first portions toward saidperipheral portions; v

i. the interior of said inner member between said first and secondportions defining a second elongated cavity means, whereby smoke passingthrough said filter element between opposite ends thereof must travelthrough both said cavity means and through said filtering material.

6. The filter rod of claim 5 wherein said filter element has a pressuredrop no greater than about 2.5 inches of water and a total particulatematter filtration efficiency of at least about 60 percent.

7. The filter rod of claim 6 wherein said filter element has a totalparticulate matter filtration efficiency of at least percent.

8. The filter rod of claim 5 wherein said filtering material comprisesat least about 25 weight percent secondary cellulose acetate.

9. The filter rod of claim 8 wherein said 'filtering material comprisesa blend of secondary cellulose acetate and pulp.

10. The filter rod of claim 5 wherein said filtering material comprisesa tubular layer of fibrous filtering material in sheet form carrying asorbent particulate filtering material.

11. The filter rod of claim 10 wherein said sorbent particulatefiltering material is activated carbon.

12. The filter rod of claim 5 wherein said filtering material comprisesa pair of tubular layers of fibrous filtering material in sheet formwith a sorbent particulate filtering material therebetween.

13. The filter rod of claim 12 wherein said sorbent particulatefiltering material is activated carbon. I

14. The filter rod of claim 5 wherein said second area is defined by oneof said end portions of said inner member being open.

15. The filter rod of claim 5 wherein said second area is defined by aplug of material extending across one of said end portions of said innermember, said plug beingformed of a material offering less resistance topassage of smoke than the area between said peripheral portions of saidinner member and said inner surface of said outer member.

16. The filter rod of claim 15 further including a quantity of a furthersmoke-modifying material carried in said second cavity means betweensaid first portions and said plug.

17. The filter rod of claim 16 wherein said further smokemodifyingmaterial is a loose, sorbent, particulate filtering material.

18. The filter rod of claim 17 wherein said sorbent particulatefiltering material is activated carbon.

19. The filter rod of claim 5 wherein said peripheral portions of saidinner member are formed by integral flared portions of said inner memberatone of said end portions of said inner member.

20. The filter rod of claim 5 wherein said first area is defined byintegral portions of said inner member crimped together at one of saidend portions of said inner member.

21. The filter rod of claim 20 wherein said crimped portions are sealedtogether by a bonding means.

22. The filter rod of claim 20 wherein spaced parts of the periphery ofsaid crimped portions contact said inner surface of said outer member toassist in centering said inner member within said outer member to assistin centering said inner member. within said outer member and in definingsaid first cavity means.

2 3.-T he filter rod of claim 22 wherein said spaced parts of theperiphery of said crimped portions contact said inner surface of saidouter member only at said one end portions of said inner member, theentire outer surface of said inner member being spaced from said innersurface of said outer member except at said spaced end portions.

24. The filter rod of claim wherein said inner member is tubular, theouter surface of one end portion of said inner member defining saidperipheral portions, the other end portions of said inner member beingcrimped and sealed together to define said first area, spaced parts ofthe periphery of said crimped portions contacting said inner surface ofsaid outer member to assist in centering said inner member within saidouter member and in defining said first cavity means, the inner surfaceof said one end portion of said inner member being open to define saidsecond area.

25. The filter rod of claim 24 wherein said spaced parts of theperiphery of said crimped portions contact said inner surface of saidouter member only at said other end portions of said inner member, theentire outer surface of said inner member being spaced from said innersurface of said outer member except at said spaced end portions 26. Thefilter rod of claim 25 wherein said other end portion of said innermember is crimped to form a generally S-shaped cross section, only thelaterally terminal edges of the S-shaped portions and said peripheralportions of said outer surface of said inner member contacting saidinner surface of said outer member.

27. The filter rod of claim 25 wherein said other end portion of saidinner member is crimped to form a generally cruciform-shaped crosssection, only the laterally terminal edges of the cruciform-shapedportions and said peripheral portions of said outer surface of saidinner member contacting said carrying a bonding means sealing saidcrimped portions of said inner member.

30. The filter rod of claim 25 wherein said inner surface of said innermember comprises a porous thermoplastic material and said outer surfaceof said inner member comprises filtering material, said thermoplasticmaterial defining a bonding means sealing said crimped portions of saidinner element.

31. The filter rod of claim 30 wherein said inner surface of said innermember is formed of a helically wound strip of said thermoplasticmaterial and said outer surface of said inner member is formed of ahelically wound strip of said filtering material overlying saidthermoplastic material, juxtaposed edges of said helically wound stripof said filtering material I being axially offset with respect tounderlying juxtaposed edges of said helically wound strip of saidfiltering material being axially offset with respect to underlyingjuxtaposed edges of said helically wound strip of said thermoplasticmaterial.

2. A filter means including a filter element comprising a. an axiallyelongated outer member; b. an axially elongated inner member disposedwithin said outer member; c. said outer member including an innersurface and an outer surface and having spaced end portions; d. saidinner member comprising a filtering material and including an innersurface and an outer surface and having spaced end portions; e. integralperipheral portions of said outer surface of said inner member beingjuxtaposed to portions of said inner surface of said outer member to atleast substantially preclude axial passage of smoke across the areatherebetween; f. the major portions of said outer surface of said innermember being spaced from said inner surface of said outer member todefine first elongated cavity means therebetween; g. integral firstportions of said inner member defining a first area extending across theinterior of said inner member which offers at least as much resistanceto passage of smoke as said filtering material, said first portionsbeing axially spaced from said peripheral portions; h. second portionsof said inner member defining a second area extending across theinterior of said inner member which offers less resistance to passage ofsmoke than the area between said peripheral portions of said innermember and said inner surface of said outer member, said second portionsbeing axially spaced from said first portions toward said peripheralportions; i. the interiOr of said inner member between said first andsecond portions defining second elongated cavity means, whereby smokepassing through said filter element between opposite ends thereof musttravel through both said cavity means and through said filteringmaterial; j. the wall of the inner member comprising filtering material,the packing density of which lies between 0.1 and 0.4.
 3. A filter meansincluding a filter element comprising: a. an axially elongated outermember; b. an axially elongated inner member disposed within said outermember; c. said outer member including an inner surface and an outersurface and having spaced end portions; d. said inner member comprisinga filtering material and including an inner surface and an outer surfaceand having spaced end portions; e. integral peripheral portions of saidouter surface of said inner member being juxtaposed to portions of saidinner surface of said outer member to at least substantially precludeaxial passage of smoke across the area therebetween; f. the majorportions of said outer surface of said inner member being spaced fromsaid inner surface of said outer member to define first elongated cavitymeans therebetween; g. integral first portions of said inner memberdefining a first area extending across the interior of said inner memberwhich offers at least as much resistance to passage of smoke as saidfiltering material, said first portions being axially spaced from saidperipheral portions; h. second portions of said inner member defining asecond area extending across the interior of said inner member whichoffers less resistance to passage of smoke than the area between saidperipheral portions of said inner member and said inner surface of saidouter member, said second portions being axially spaced from said firstportions toward said peripheral portions; i. the interior of said innermember between said first and second portions defining second elongatedcavity means, whereby smoke passing through said filter element betweenopposite ends thereof must travel through both said cavity means andthrough said filtering material; j. the wall of the inner membercomprising substantially of fibers having a diameter of less than 25microns.
 4. A filter means including a filter element comprising a. anaxially elongated outer member; b. an axially elongated inner memberdisposed within said outer member; c. said outer member including aninner surface and an outer surface and having spaced end portions; d.said inner member comprising a filtering material and including an innersurface and an outer surface and having spaced end portions; e. integralperipheral portions of said outer surface of said inner member beingjuxtaposed to portions of said inner surface of said outer member to atleast substantially preclude axial passage of smoke across the areatherebetween; f. the major portions of said outer surface of said innermember being spaced from said inner surface of said outer member todefine first elongated cavity means therebetween; g. integral firstportions of said inner member defining a first area extending across theinterior of said inner member which offers at least as much resistanceto passage of smoke as said filtering material, said first portionsbeing axially spaced from said peripheral portions; h. second portionsof said inner member defining a second area extending across theinterior of said inner member which offers less resistance to passage ofsmoke than the area between said peripheral portions of said innermember and said inner surface of said outer member, said second portionsbeing axially spaced from said first portions toward said peripheralportions; i. the interior of said inner member between said first andsecond portions defining second elongated cavity means, whereby smokepassing through said filter element between opposite ends thereof musttravel through Both said cavity means and through said filteringmaterial; j. the pressure drop being not greater than 6 cm. water gauge.5. A filter rod comprising a plurality of filter means integrally joinedin end-to-end relationship for subsequent separation, said filter meanscomprising: a. an axially elongated outer member; b. an axiallyelongated inner member disposed within said outer member; c. said outermember including an inner surface and an outer surface and having spacedend portions; d. said inner member comprising a filtering material andincluding an inner surface and an outer surface and having spaced endportions; e. integral peripheral portions of said outer surface of saidinner member being juxtaposed to portions of said inner surface of saidouter member to at least substantially preclude axial passage of smokeacross the area therebetween; f. the major portions of said outersurface of said inner member being spaced from said inner surface ofsaid outer member to define first elongated cavity means therebetween;g. integral first portions of said inner member defining a first areaextending across the interior of said inner member which offers at leastas much resistance to passage of smoke as said filtering material, saidfirst portions being axially spaced from said peripheral portions; h.second portions of said inner member defining a second area extendingacross the interior of said inner member which offers less resistance topassage of smoke than the area between said peripheral portions of saidinner member and said inner surface of said outer member, said secondportions being axially spaced from said first portions toward saidperipheral portions; i. the interior of said inner member between saidfirst and second portions defining a second elongated cavity means,whereby smoke passing through said filter element between opposite endsthereof must travel through both said cavity means and through saidfiltering material.
 6. The filter rod of claim 5 wherein said filterelement has a pressure drop no greater than about 2.5 inches of waterand a total particulate matter filtration efficiency of at least about60 percent.
 7. The filter rod of claim 6 wherein said filter element hasa total particulate matter filtration efficiency of at least 90 percent.8. The filter rod of claim 5 wherein said filtering material comprisesat least about 25 weight percent secondary cellulose acetate.
 9. Thefilter rod of claim 8 wherein said filtering material comprises a blendof secondary cellulose acetate and pulp.
 10. The filter rod of claim 5wherein said filtering material comprises a tubular layer of fibrousfiltering material in sheet form carrying a sorbent particulatefiltering material.
 11. The filter rod of claim 10 wherein said sorbentparticulate filtering material is activated carbon.
 12. The filter rodof claim 5 wherein said filtering material comprises a pair of tubularlayers of fibrous filtering material in sheet form with a sorbentparticulate filtering material therebetween.
 13. The filter rod of claim12 wherein said sorbent particulate filtering material is activatedcarbon.
 14. The filter rod of claim 5 wherein said second area isdefined by one of said end portions of said inner member being open. 15.The filter rod of claim 5 wherein said second area is defined by a plugof material extending across one of said end portions of said innermember, said plug being formed of a material offering less resistance topassage of smoke than the area between said peripheral portions of saidinner member and said inner surface of said outer member.
 16. The filterrod of claim 15 further including a quantity of a furthersmoke-modifying material carried in said second cavity means betweensaid first portions and said plug.
 17. The filter rod of claim 16wherein said further smoke-modifying material is a loose, sorbent,particulate filtering material.
 18. The filter rod of claim 17 whereinsaid sorbent particulate filtering material is activated carbon.
 19. Thefilter rod of claim 5 wherein said peripheral portions of said innermember are formed by integral flared portions of said inner member atone of said end portions of said inner member.
 20. The filter rod ofclaim 5 wherein said first area is defined by integral portions of saidinner member crimped together at one of said end portions of said innermember.
 21. The filter rod of claim 20 wherein said crimped portions aresealed together by a bonding means.
 22. The filter rod of claim 20wherein spaced parts of the periphery of said crimped portions contactsaid inner surface of said outer member to assist in centering saidinner member within said outer member and in defining said first cavitymeans.
 23. The filter rod of claim 22 wherein said spaced parts of theperiphery of said crimped portions contact said inner surface of saidouter member only at said one end portions of said inner member, theentire outer surface of said inner member being spaced from said innersurface of said outer member except at said spaced end portions.
 24. Thefilter rod of claim 5 wherein said inner member is tubular, the outersurface of one end portion of said inner member defining said peripheralportions, the other end portions of said inner member being crimped andsealed together to define said first area, spaced parts of the peripheryof said crimped portions contacting said inner surface of said outermember to assist in centering said inner member within said outer memberand in defining said first cavity means, the inner surface of said oneend portion of said inner member being open to define said second area.25. The filter rod of claim 24 wherein said spaced parts of theperiphery of said crimped portions contact said inner surface of saidouter member only at said other end portions of said inner member, theentire outer surface of said inner member being spaced from said innersurface of said outer member except at said spaced end portions.
 26. Thefilter rod of claim 25 wherein said other end portion of said innermember is crimped to form a generally S-shaped cross section, only thelaterally terminal edges of the S-shaped portions and said peripheralportions of said outer surface of said inner member contacting saidinner surface of said outer member.
 27. The filter rod of claim 25wherein said other end portion of said inner member is crimped to form agenerally cruciform-shaped cross section, only the laterally terminaledges of the cruciform-shaped portions and said peripheral portions ofsaid outer surface of said inner member contacting said inner surface ofsaid outer member.
 28. The filter rod of claim 25 wherein said other endportion of said inner member is crimped to form a generally Y-shapedcross section, only the laterally terminal portions of the Y-shapedportions and said peripheral portions of said other surface of saidinner member contacting said inner surface of said outer member.
 29. Thefilter rod of claim 25 wherein said inner member includes a tubularelement comprising filtering material, said inner surface of said otherend portion of said tubular element carrying a bonding means sealingsaid crimped portions of said inner member.
 30. The filter rod of claim25 wherein said inner surface of said inner member comprises a porousthermoplastic material and said outer surface of said inner membercomprises filtering material, said thermoplastic material defining abonding means sealing said crimped portions of said inner element. 31.The filter rod of claim 30 wherein said inner surface of said innermember is formed of a helically wound strip of said thermoplasticmaterial and said outer surface of said inner member is formed of ahelically wound strip of said filtering material overlying saidthermoplastic material, juxtaposed edges of said helically wound stripof said filtering material beinG axially offset with respect tounderlying juxtaposed edges of said helically wound strip of saidfiltering material being axially offset with respect to underlyingjuxtaposed edges of said helically wound strip of said thermoplasticmaterial.